We will utilize already-existing data that have been obtained by the NHLBI- sponsored Resuscitation Outcomes Consortium (ROC). Although the ROC generates vast quantities of resuscitation data, ROC investigators have been unable to maximize these due to the labor-intensive nature of the type of work we propose. Studying patients who experience out-of-hospital cardiac arrest, we will determine the incidence of re-arrest in patients who achieve a return of spontaneous circulation (ROSC) during the prehospital phase of their care. We believe that by developing a better understanding of the incidence and outcomes of re-arrest, the electrocardiographic (ECG) characteristics that indicate impending re-arrest, and clinical variables that affect re-arrest, more patients can be helped to survive. PUBLIC HEALTH RELEVANCE: We are proposing to use already-existing data from the Resuscitation Outcomes Consortium (ROC) in order to determine the incidence of re-arrest in patients who suffer an out-of-hospital cardiac arrest, after getting a pulse back during their pre-hospital care. We will also determine their clinical outcomes (admission to the hospital and survival). We will determine whether information contained in the electrocardiogram (ECG) can be used to identify which patients are likely to re-arrest.